Polyethylene naphthalate (PEN) has physical properties which makes it highly desirable for utilization in making a wide variety of articles. For instance, PEN can be molded into bottles for carbonated beverages which have outstanding gas barrier characteristics and heat stability. The outstanding gas barrier characteristics of PEN make it a viable candidate as a material for manufacturing bottles for beverages which are highly sensitive to oxygen, such as beer. Its high melting point also makes it suitable for use in manufacturing beverage bottles which can be recycled and sterilized at elevated temperatures. PEN also has an excellent combination of properties for utilization in making food trays which are suitable for use in either convection ovens or microwave ovens.
PEN does not crystallize rapidly at temperatures which are normally utilized in standard molding operations. In fact, PEN has a maximum crystallization rate at about 195.degree. C. This very high crystallization peak temperature associated with PEN necessitates the utilization of high molding temperatures to achieve reasonable molding cycle times. Unfortunately, the utilization of such high molding temperatures results in equipment problems and higher costs. Molding PEN at standard molding temperatures is generally not a viable commercial option because the slow crystallization rates attained dictate the use of unacceptably long cycle times.